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Best rotary switch for an attenuator?

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  • #1

    Best rotary switch for an attenuator?

    I'm working on a simple resistive attenuator, I've bought the necessary power resistors at the local surplus store (all cement boxes), but I'm having a problem finding a proper switch.

    I need at least a 3-position switch for 3 levels of attenuation.
    A 4P one would be nice to add an additionnal level of attenuation, and a 5P would allow a bypass option on top of that (although I can always use a separate one for that.
    It has to be double-pole since it needs to switch two circuits at once (one branch of the L-Pad goes up while the other goes down)

    I've tried finding what I need on Mouser but finding a DP3T with the proper current ratting (need at least 2A) isn't easy.

    I've found the following slide switch
    46313LDRX

    They don't specify if it's shorting or not though... (shorting would be best to allow switching while the amp is on)

    Shorting rotary switches would be the best, but I really can't find the proper combination of double-pole, 2A, and 3 to 5 positions in rotary style...

    Any suggestions?
    Tags: None
  • #2
    I ended up using a rheostat for my design. But I originally wanted a switch. I did find one. It was a 2P6T IIRC, but unfortunately I can't remember where. If it helps I recall it was an appliance part like you would find in a washing machine or a wall heater. I also remember that Mouser carried it but I just can't remember how I ran across it. But this is the kind of part application you need to search for. I'm trying to remember how I located it and If I do I'll let you know.

    Chuck
    "Take two placebos, works twice as well." Enzo

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "If you're not interested in opinions and the experience of others, why even start a thread?
    You can't just expect consent." Helmholtz

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    • #3
      Nebraska Surplus has a nice old heavy duty
      Rotary Switch
      2P6T - Silver (SWR) 3126J, Make Before Break with heavy silver contacts for $9, no word on the current handling but it looks beefy.

      I got the DP3T (SWR) 3123J Mallory version with shorting contacts and it does a couple amps no problem, since its shorting some conductive grease can help with the current handling IME.

      find them here:
      Rotary Switches: All Other

      Dayton audio makes a attenuator with resistors that you could hack, its rated to 60watts but its spendy and looks light weight: http://www.parts-express.com/pdf/300-556m.pdf

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      • #4
        O.K. I did find the part, It's made by C&K but...

        It's a non-shorting switch (part# A20615RNZQ). C&K makes the same switch with shorting contacts (part# A20615RSZQ) but I can't find one for sale.

        This was fine with me at the time because I was considering building these attenuators in quantity. So I could have ordered the part from one of the "min. order 100" type places like Digikey.

        You may consider bridging a larg-ish resistor (like 100 ohms) across the switching assembly. Or design so that the switch creates resistor combinations for a net resistance instead of entirely different resistors for each position. That way you could use a non-shorting switch.

        Good luck

        Chuck
        "Take two placebos, works twice as well." Enzo

        "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

        "If you're not interested in opinions and the experience of others, why even start a thread?
        You can't just expect consent." Helmholtz

        Comment

        • #5
          Originally posted by Chuck H View Post
          O.K. I did find the part, It's made by C&K but...

          It's a non-shorting switch (part# A20615RNZQ). C&K makes the same switch with shorting contacts (part# A20615RSZQ) but I can't find one for sale.

          This was fine with me at the time because I was considering building these attenuators in quantity. So I could have ordered the part from one of the "min. order 100" type places like Digikey.

          You may consider bridging a larg-ish resistor (like 100 ohms) across the switching assembly. Or design so that the switch creates resistor combinations for a net resistance instead of entirely different resistors for each position. That way you could use a non-shorting switch.

          Good luck

          Chuck
          Great, that's exactly what I need!!! Many thanks

          I've reworked my circuit and I can do without the "shorting" part.

          Comment

          • #6
            hey at tubesandmore.com they have this 1p3t rotary switch. Part is P-H600 Will work great for 4/8/16 ohm options for an attenuator. Hard wire all your parallel and series power resistors to the speaker +/-. Then just connect the parallel and series resistors together at the ends that are opposite from the speaker for your 3 ohm options, then use the switch to select one. I'm building one that is half power for the 3 z options.

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